Selective signaling system



Jan. 7, 1930. THOMPSQN 1,742,291

SELECTIVE SIGNALING SYSTEM Filed March 11 1925 INVENTOR 61E flaw M9010 I BY W ATTORNEY Patented Jan. 7, 1930 UNITED STATEOS- r-A'rsrrr oFncE GEORGE K. THOMPSON, OF MAPLEWOOD, JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK snnncrrv'n SIGNALING sYs'rnn Application filed March n, 1925. smai'm. 14,767.

This invention relates to selective signalin systems and more particularly to s stems o the character which are adapted or use in connection with multi-station telephone lines;

It is an object of this invention .to provide means for selectively signaling any one of the subscribers on a multi-party line without disturbing the others.

' Another object is to provide means for signaling at carrier frequencies over either a voice or carrier frequency telephone system. These objects of the invention and certain other. features thereof set forth below are attained as described in the following specification which has reference to certain specific embodiments of the invention illustrated in theaccompanying diagram, in which Fi re. 1 is a diagrammatic view of one form an arrangement embodying the invention and Fig. 2 is a diagrammatic view of an application of v the embodiment of the invention to selective ringing on inulti-party lines.

Referring to Fig. 1, the reference character L designates a telephone line havlng associated therewith at one end two sources of current supply 1 and 2, and bridged across the line at the other end a signalingdevice 3.

Two currents having frequencies above the audible range, such as 30,000 and 31,000 cycles, and diiferin in frequency by a value such as 1,000 cycles, are applied at station A to the conductors of the telephone line L. At B, a subscribers station, there is located a signaling device consisting of a coil or an electro-magnot having a non-magnetized or slightly magnetized iron core actuating either an armature of a hell or a diaphragm, such as is employed in telephone receivers and loud speakers, which armature or diaphragm is tuned to vibrate freel at about 1,000 cycles.

- The signa ing device is essentially an electromagnet and armature upon which a ma netic field acts due to the current in the hehx wound about part or allof the core of the lowing form:

electromagnet. If at an instant the current the helix is I, then t e force Pulling the diaphragm or armature toward the electro magnet is P=KI2 1 where K is a constant depending upon the physical structure.

The transmission of signals in accordance with this invention is characterized by such complex physical processes that an analysis of the phenomena involved seems best ada ti or ed to the elucidation of the invention. simplicity, this analysis will be limited to the case of transmission of two high frequencies 21r I conveniently represented by the mathematical expressions I sin pt and I sin gt. If the expressions of the values of thecurrents in line L be substituted in Equation (ll) it will and The two currents may then be be found that P= Km sin pt+ 1, sin ot 2 Expanding this expression it will result that 2 2 P= Z 5 cos 2 pt+2KI I sin.

i 2 i '3 pt sin qt+ 1 5 5- cos 2 qt (4) And by another trigonometrical transformation equation (4) may bewritten in the folthe purposes of this analysis. The second and last terms of this expression are of a double frequency and if and are inaudible frequencies, then these are also inaudible. The third term is of a frequency which is equal to the sum of the frequencles ofthe transmitted currents and obviously is also in- I audible. The fourth term K1 1 cos (p- )t is of a frequency which is equal to the di erence between the frequencies of the currents in line L and is the one on which the opera-' tion of this arrangement depends, re resenting the useful energy. Except for t smatter'of phase, the fact that th1s expression 1s a cosine rather than a sine has no significance. Thus -two currents having frequencies above t e audible range and differing in frequency by a value within the audible range are apphed'to the line L to produce at the signaling device, employed asa demodulator, two forces which, in combination, move its diaphragm at'a frequency equal to the difference in the frequencies of the high frequency currents. By properly choosing the frequen-, cies of the signaling currents it is possible to produce a si al of suitable'low';frequency without app ying to the line any frequency within the audible. range.

Fig. 2 represents an embodiment of th1s invention asapplied to selective ringing on multi-party lines. -By properly selecting the oscillator frequencies at the central office and by employing suitable band filters at the sub scribers stations it is possible to signal any one of a plurality of subscribers without disturbing the others. For example, a station having interposed between the line and signaling device aband filter which passes only frequencies between 20,000 and 25,000 cycles may be signaled by currents having frequencies of 22,000 and 23,000 cycles without affecting any other subscriber, if no other subscriber on the line has a filter of the same limits. Other subscribers may be signaled by using frequencies within the limits of their band filters. It will be understood that the frequencies .hereinbefore described are merely illustrative and may be varied in practice as conditions may require.

It will also be understood that the details of the arrangements herein set forthmay be varied and the general principles herein disclosed may be embodied in many other organizations widely different from those illus-' trated without-departing from the spirit of the invention or the scope of the appended u I I What is claimed is:

1. The method of high frequency telephonic signaling over a telephone line which consists in generatin a plurality of pairs of high fr uency osci ations, all of which are sinusoida waves, impressin all of said oscillations on said telephone line, and effecting mechanical vibrations corresponding to each pair of said high frequency oscillations after transmission over said telephone line to produce signals of frequencies equal to the differences between the corresponding pairs of I high frequency oscillations, said signals being of frequencies within the limits of audibility.

2. In a high frequency signaling system, the combination of sources of energy generating a pair of continuous, high frequency, undamped carrier waves, an untuned trans- .ll'llSSlOl'l circuit upon which said high frequency waves are superposed, and electromagnetic means for receiving said high frequency waves to produce mechanical vibrations of a frequency within the audible range, said generated high frequency carrier waves differing from each other by a frequency within the limits of said receiving means.

- 3. In combination, means for generating a pair of unmodulated carrier waves, an unt-uned circuit for transmitting said carrier waves, and a receiver of the electromagnetic type for-translating said carrier waves into audible signals.

4.-In combination, means for generating two unmodulated high frequency waves differing in frequency by an amount within the limits of audibilit-y, an untuned medium for transmitting said'waves, a filter for suppressing undesired waves and for freely transmitting said unmodulated high frequency waves, and electromagnetic means for converting the signals represented by said high frequency waves into audible mechanical vibrations.

5. In a signaling system, in combination, a plurality of carrier currents, a plurality of signaling devices, means for transmitting said carrier currents to said signaling devices, and a plurality of band filters, each band filter selecting a pair of said carrier currents within-its limits to the exclusion of all other carrier currents, each pair of said carrier currents being employed to operate a signaling device.

' 6. A multiplex signaling system comprising a common transmission line, means for transmitting sinusoidal waves of different high frequencies thereover, an individual circuit for each pair of said high frequency sinusoidal waves, separate selective means con necting each of said circuits to said line, said selective means comprising filters connected effectively in parallel to each other with respect to said line, each of said selective means passing only one pair of said high frequency sinusoidal waves and effectively suppressing all other currents, and electromagrlietic means associated with each filter of t e selective means for obtainin a magnetic pull of a frequency equal to t e difference of the frequencies of each pair of sinusoidal waves. v

7. In a multiplex Signaling system, in combination, a line, means to impress a plurality of sinusoidal currents of differeht frequencies upon said line, said sinusoidal currents being grouped into pairs, each pair differing in requency by a predetermined amount, selec tive nieans consisting of band filters. connected in parallel to each other with respect to said line,.and means of the electroma netic type. operativel associated with eac pair of said sinusoi al currents impressed upon said line.

8. In a carrier current signaling system, a high frequency line, a plurality of electromagnetic devices connected thereto, means for impressin on said high frequency line a plurality of igh frequency sinusoidal currents, and individual band filters'conn'ecting each electromagpetic device to said high frequency line, eac band filter passing only two of said high frequency sinusoidal currents to the exclusion of the others, the two high frequency sinusoidalcurrents being related so as to operate said electromagnetic devices.-

9. In a multiplex signalin system, a line adapted for carryingv a plum ity of high frequency currents, means forproducing a plurality of high frequency sinusoidal waves for transmission over said line, a plurality of electromagnetic receivers, each electromagnetic receiver being employed for receiving signals transmitted by each pair of said high frequency sinusoidal waves, and a plurality of band filters each selectively passing the high frequency sinusoidal waves employed in the'transmission of a different signal to each electromagnetic receiver.

10. A multiplex signaling system comprising a common transmission line, means for transmitting a plurality of currents ,of high frequencies thereover, each pair of saidcurrents differing in frequency by an amount within the limits of audibility, an individual circuit for each pair of said high frequency currents, separate selective means connecting each of said circuits to said line, said selective means comprising filters connected effectively in parallel to each other with respect to said line, each of said selective means passing one pair of said high frequency currents to the exclusion of all other currents, and electromagnetic demodulating means responsive to each pair of said currents, each pair of said currents producing a magnetic pull which has a frequency equal to the difference between the frequencies of the currents of said pair and whichoperates the corresponding electromagnetic demodulating means. I

11. A multiplex signaling system comprisquency currents, each pair of said carrier currents differing in frequency by a predetermined amount, selective means for each air of said carrier currents connected to said 'ne, and a plurality of receivers acting as demodulators, one 0 said receivers being provided for each pair of carrier currents, each pair of said carrier currents producin a magnetic pull of a frequency equal to the ifierence between the frequencies of the carrier currents of said pair and suflicient to operate the corresponding receiver.

12. In a signaling system, a. air of intercommunicating stations, a plura ity of si almg channels at one station, a plurality of orresponding signaling channels at the other station, an electromagnetic device in each of said second-mentioned channels, and means whereby pairs of high fre uencysignaling currents may be transmitted rom each of said first-mentioned channels to the distant station and applied to the corresponding electromagnetic device, one pair of said high frequency currents being 1m ressed upon each electromagnetic deviceand producing a magnetic 'pull in the correspondin electromagnetic device of a frequency equa to the difference between the frequencies of the impressed March 1925.

GEORGE K, THOMPSON. 

